functional-tester/tester: use "*clientv3.Client" for lease stresser
functional-tester/tester: use "*clientv3.Client" for lease stresser

Signed-off-by: Gyuho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

mkumatag/etcd,mqliang/etcd,sebrandon1/etcd,ajityagaty/etcd,etcd-io/etcd,sebrandon1/etcd,bdarnell/etcd,li-ang/etcd,glevand/coreos--etcd,dannysauer/etcd,vimalk78/etcd,xiang90/etcd,bdarnell/etcd,rnaveiras/etcd,coreos/etcd,ajityagaty/etcd,etcd-io/etcd,sinsharat/etcd,rnaveiras/etcd,cockroachdb/etcd,fanminshi/etcd,ajityagaty/etcd,mqliang/etcd,lorneli/etcd,sinsharat/etcd,gyuho/etcd,coreos/etcd,mkumatag/etcd,mqliang/etcd,lorneli/etcd,gyuho/etcd,etcd-io/etcd,joshix/etcd,dannysauer/etcd,vimalk78/etcd,rnaveiras/etcd,joshix/etcd,fanminshi/etcd,glevand/coreos--etcd,mkumatag/etcd,li-ang/etcd,cockroachdb/etcd,xiang90/etcd